Motor neuron diseases

Generality

Diseases of the motor neuron is the generic name assigned to a group of neurodegenerative conditions that specifically affect the good health and good functioning of the motor neurons.

Motor neurons are nerve cells responsible for controlling voluntary muscles, glands, part of the heart and smooth muscles.

The most known motor neuron diseases are: ALS, primary lateral sclerosis, progressive muscular atrophy, progressive bulbar paralysis and pseudobulbar paralysis.

Currently, doctors do not know the precise causes of all these diseases.

The list of symptoms of a motor neuron disease is very variable and depends on what tasks the involved motor neurons perform. For example, in ALS, the involvement of motor neurons is total, therefore, the patient complains of difficulties in various areas, from walking and speech to breathing and masticatory capacity.

The diagnosis of a motor neuron disease requires several tests, as there is no special diagnostic test.

For the moment, there are no specific treatments, but only symptomatic treatments.

What is motor neuron disease?

Motor neuron disease is the medical term for any progressive neurological degenerative condition that specifically affects nerve cells known as motor neurons or motor neurons .

In medicine, a progressive degenerative neurological condition, such as a generic neuron disease, is called neurodegenerative disease .

WHAT ARE THEY AND WHAT FUNCTIONS DO THE MOTONEURONS CARRY OUT?

Originating in the brain or spinal cord, motor neurons are the special nerve cells that, with their network of axons, control the voluntary muscles, glands, heart and smooth muscles .

The human nervous system comprises two classes of motor neurons: the upper motor neurons (or first motoneurons ) and the lower motor neurons (or second motor neurons ).

These two classes of motor neurons are comparable to two runners participating in a pair relay race. In fact, the upper motor neurons represent the first athlete (that is, the one who gives start to the race with the witness), since they are the points of elaboration and departure of the nervous signals destined to the voluntary skeletal muscles, to the glands etc. The lower motor neurons, on the other hand, represent the second athlete (that is, the one who, having received the baton from the first athlete, completes the race), as they are the reception and delivery centers for nerve signals coming from the upper motor neurons.

In essence, therefore, the upper motor neurons are the creators of those nerve signals, whose final delivery to voluntary muscles, glands etc. it is up to the lower motor neurons.

Recovering the comparison with the two relay runners, the delivery point of the witness between the upper motor neurons and the lower motor neurons is the spinal cord .

Important functions depend on the good health of human motor neurons, such as breathing, walking, swallowing, talking, holding objects, releasing glandular secretions, etc.

Types

Under the wording "motor neuron disease" fall several pathologies, all of which are clearly accumulated by the involvement of motor neurons.

Among the pathologies belonging to the group of motor neuron diseases, include:

• Amyotrophic lateral sclerosis, better known as ALS . It is the most common and famous motor neuron disease;
• Primary lateral sclerosis, also known as SLP ;
• Progressive muscular atrophy, or AMP ;
• Progressive bulbar palsy, also known as PBP ;
• Pseudobulbar paralysis ;
• Spinal muscular atrophy, also called by the acronym SMA . Its inclusion in the list of motor neuron diseases has always been uncertain and a reason for continuous debates, on the part of the medical-scientific community.

Of these types of motor neuron diseases, some are more serious than others.

Absolutely the most severe motor neuron disease is ALS.

IMPORTANT NOTICE ON "MOTONEURONE DISEASE" TERMINOLOGY

In medicine, the term "motor neuron disease" can be used as the name of a group of neurodegenerative diseases - which are the ones mentioned above - or as one of the many synonyms of ALS. There is no more correct meaning than another; however, in this article, the first option was chosen.

Causes

A motor neuron disease arises due to the degeneration and atrophy of the motor neurons . The degeneration and atrophy of the motor neurons progressively impairs their health status and their ability to control voluntary muscles, glands etc.

Today, despite numerous studies on the subject, the causes of the processes of degeneration and atrophy of the motor neurons (hence the causes of a generic motor neuron disease) remain a mystery, except for the pathological forms of genetic inheritance (eg: SMA, some subtypes of SLAs etc.).

SLA

In ALS, the degeneration and atrophy of motor neurons affect both the upper motor neurons and the lower motor neurons.

PRIMARY LATERAL SCLEROSIS

In primary lateral sclerosis, motor neuron degeneration and atrophy only affect the upper motor neurons.

PROGRESSIVE MUSCULAR ATROPHY

In progressive muscular sclerosis, the process of degeneration and atrophy of the motor neurons involves only the lower motor neurons.

PROGRESSIVE BULBAL PARALYSIS

In progressive bulbar paralysis, most scientific evidence shows that the degeneration and atrophy of motor neurons mainly involve the lower motor neurons.

PSEUDOBULBAR PARALYSIS

In pseudobulbar paralysis, the process of degeneration and atrophy of the motor neurons concerns the upper motor neurons of the brainstem, which are part of the so-called corticobulbar tract.

SMA

In SMA, degeneration and atrophy of motor neurons target some lower motoneurons.

Symptoms, signs and complications

Possible symptoms and signs of a motor neuron disease include:

• Sense of weakness and softness scattered in various parts of the body (eg: trunk, arms, hand, jaw, legs, feet, etc.);
• Problems of chewing and swallowing, and spasticity of the tongue;
• Problems in walking, balance problems and presence of spasticity in the limbs;
• Tremors in the arms;
• Inability to grip with hands;
• Recurrent muscle cramps and fasciculations;
• Difficulty in keeping the head high;
• Difficulty maintaining upright posture;
• Slurred speech (dysarthria);
• Loss of reflexes;
• Breathing difficulties.

For the avoidance of doubt, it is important to point out that the extent of the symptomatic picture depends on the type of motor neuron disease present. For example, ALS includes all the clinical manifestations listed above, while pseudobulbar paralysis includes only the clinical manifestations related to swallowing capacity, chewing ability, language and language.

COMPLICATIONS

Due to the progressive and inevitable degeneration of motor neurons, any motor neuron disease involves, in more or less long times, the onset of serious complications, some of which have a fatal outcome.

The complications in question correspond, in fact, to a marked aggravation of the various symptoms mentioned above .

Therefore, walking difficulties become a complete incapacity of the use of the legs (patients in this state, in fact, need a wheelchair); the dysarthria becomes complete lack of the use of the word (to communicate, some patients use particular electronic devices); chewing and swallowing problems get worse to the point that the patient needs medical support for artificial nutrition; breathing difficulties become total inability to breathe (patients need continuous support for spontaneous breathing); and so on.

Each motor neuron disease has very different times and modes of symptom evolution.

For example, in the case of ALS, the final stage of the disease occurs after 1-3 years from the appearance of the first symptoms; in bulbar progressive paralysis, already after 6 months; in primary lateral sclerosis, after one or two decades; in the WAP, after 2-4 years; etc.

MAIN CAUSE OF DEATH

In most patients with a potentially lethal neuron disease (eg, ALS or progressive bulbar paralysis), death occurs due to severe respiratory failure or severe pneumonia .

Diagnosis

Currently, there is no highly specific diagnostic test, which allows a certain motor neuron disease to be identified with certainty.

Therefore, to diagnose a motor neuron disease, doctors must resort to different tests, some of which also aim to exclude pathologies with similar symptoms (differential diagnosis).

The tests for the diagnosis of a motor neuron disease include:

• The physical examination;
• Electromyography and tests on nerve conduction velocity;
• Laboratory tests on blood and urine;
• Magnetic resonance imaging and / or CT scan of the brain and spinal cord (for differential diagnosis);
• Muscle biopsy (for differential diagnosis);
• Lumbar puncture (for differential diagnosis).

Therapy

At the present time, any motor neuron disease is an incurable condition, in the sense that there are neither cures capable of stopping the progressive degeneration of motor neurons nor, even less, treatments capable of healing the degenerated motor neurons.

The only treatments that people with a motor neuron disease can rely on are symptomatic (or symptomatic ) therapies . As can be guessed, a symptomatic therapy is a therapy aimed at alleviating one or a series of symptoms, so as to improve the quality of life of the patient.

Symptomatic therapies for motor neuron diseases vary according to the symptoms present: for example, if a motor neuron disease compromises gait and chewing and swallowing abilities, the patient will need a support to walk or move (eg: crutches or chair on wheels ) and a support to nutrition (ex: artificial nutrition )

The effectiveness of symptomatic therapies depends on the severity of the motor neuron disease present: there are motor neuron diseases whose symptomatology is more treatable than in other cases.

Prognosis

Motor neuron diseases cause irreversible and incurable damage to the nervous system, severely affect the quality of life of patients and, in certain forms, are lethal.

All this explains why, in the presence of a generic motor neuron disease, doctors usually outline an unfavorable prognosis.